1. Field of the Invention
The present invention relates to an electronic component mounting method and apparatus for mounting an electronic component on a circuit board with high precision, an electronic component mounting system, an electronic component mounting data creating method, a mounting data creating device, and a program to be used therein. More particularly, the invention relates to a technique for carrying out mounting by effectively utilizing a self-alignment effect without a failure in mounting even if there is a small interval between mounting positions of electronic components on the circuit board
2. Description of the Related Art
As shown in FIG. 29, for example, the process for manufacturing a circuit board on which an electronic component mounted includes three steps. The first step is a printing step (1) of printing a solder paste on a circuit board having a land formed thereon by means of a solder paste printing apparatus. The next step is a inspecting step (2) of inspecting the print state of the solder paste by means of a inspecting apparatus. The last is a mounting step (3) of mounting an electronic component on the circuit board by means of an electronic component mounting apparatus. The solder paste printing apparatus, the inspecting apparatus and the electronic component mounting apparatus are connected in this order over a manufacturing line respectively, and the circuit board fed to the manufacturing line is taken out through the steps (1), (2) and (3) and is sent to a reflow step which is not shown.
Recently, a mounting interval between electronic components to be mounted on a circuit board is reduced to approximately 0.15 mm and the same interval will tend to be reduced increasingly in the future. In order to reduce an interval between components to be mounted, the soldering state of the electronic component has been fillet-less. In order to make the state fillet-less, it is necessary to prevent “extension wetting” in which a molten solder overflows and occurs “solder elevation” along the end face of the terminal of the electronic component as shown in FIG. 30(b). The “solder elevation” is a phenomenon that a molten solder paste trickles upward along a electronic component when the electronic component is mounted on the solder paste. The “solder elevation” causes the “extension wetting” which causes generation of bridges between electronic components. Therefore, the width of a land to be formed on the circuit board is set to be equal to or smaller than the width of the terminal of the electronic component such that the overflowed solder does not pollute the end face of the terminal. More specifically, an excessive solder does not stick to the end face of the terminal by setting the width of the land to be equal to or smaller than the width of the terminal of the electronic component. Consequently, it is possible to prevent the solder from extensively overflowing from a terminal surface on the land side.
When an electronic component is to be soldered to the land, a solder paste is printed on the land and the electronic component is mounted in alignment with the position of the land, and a reflow process is then carried out. By the reflow process, the solder paste interposed between the land and the terminal of the electronic component is molten and fluidized. The electronic component is also moved to the center position of the land by a self-alignment effect. Consequently, mounting is carried out while positioning of the land is performed.
In the conventional soldering method, however, the mounting is carried out with a target mounting position of the electronic component in alignment with the position of the land. Therefore, in the case in which the printing position of the solder paste is shifted from the position of the land, there is a problem in that a failure in soldering is occurred after the reflow process. FIG. 31(a) shows a state in which the electronic component is mounted, in alignment with the center position of each land, on the circuit board having the solder paste printed with a shift from the position of the land. FIG. 31(b) shows a result obtained by carrying out the reflow process over the circuit board.
In the case in which a positional relationship between the mounted electronic component and the printed solder paste is such that the solder paste is protruded from the end of the electronic component as shown, “extension wetting” is occurred between the solder and the end of the electronic component during the reflow process. As a result, the solder unnecessarily floods over the side surface of the terminal of the electronic component so that a bridge is generated between the adjacent electronic components or terminals. The bridge is not generated if the mounting interval between the electronic components is wide. However, the bridges are generated frequently in the circuit board having small intervals between the electronic components particularly that causes a remarkable decline in quality of the circuit board on which is mounted electronic components.
Moreover, a solder paste printing apparatus can finely control the position of a land of a circuit board and a printing position of solder paste. However, it is hard to uniformly carry out alignment over the whole circuit board having small mounting internals of electronic components, and substantially, it is very hard to completely correct a local shift.